Flexible natural wood sheet

ABSTRACT

A flexible natural wood sheet excellent in softness and folding endurance, which is obtained by overcoming a disadvantage of a thin natural wood plate material that it is easily cracked or broken, without loosing texture and feeling inherent to natural wood, is provided. Cavities in the thin natural wood plate material are filled with a polymer compound to impart softness and folding endurance to the thin natural wood plate material. At the same time, the surface of the thin natural wood plate material is not entirely covered by filling the polymer compound. Accordingly, the problem can be solved.

TECHNICAL FIELD

[0001] The present invention relates to a flexible natural wood sheetexcellent in softness and folding endurance, which is suitable for useas a material of small articles such as a bag or a pouch.

BACKGROUND ART

[0002] Conventionally, in order to process natural wood in a sheet andto use the sheet to fabricate small articles such as a bag, a handbag, awallet, a coin purse, a book cover, a cover sheet, a belt or a pouch, itis necessary to use the natural wood as a soft thin plate. However, whenwood, which is a naturally-occurring polymer, is dried, the wood istransformed into a glassy polymer in which a brittle fracture is likelyto occur. Thus, a thin plate material is more frequently cracked orbroken by bending, a contact or the like. Accordingly, in order to use athin natural wood plate material, the efforts have been made using somesort of method such as attachment of a flexible film made of polyvinylchloride or the like, coating on either or both of the surfaces of thethin plate material, or reinforcement with a reinforcing material sothat the thin plate material is not cracked or broken even if a brittlefracture occurs.

[0003] If a flexible film is attached to a thin natural wood platematerial, a flexible film is used to form a laminate structure, or athin natural wood plate material is coated as described above, thesurface of the thin natural wood plate material is covered with asynthetic resin contained in the film or the coating agent. Therefore,there arises a problem that texture and feeling inherent to natural woodare lost.

[0004] Moreover, although the use of a reinforcing material such as aflexible film greatly contributes to the folding endurance of thereinforcing material such as a film, it does not improve the foldingendurance of a thin natural wood plate material.

[0005] On the other hand, if a thin natural wood plate material isintended to be used for a small article such as a bag or a pouch byutilizing the texture inherent to natural wood, wood consisting of anaturally-occurring polymer is transformed into a glassy polymer inwhich a brittle fracture is likely to occur when it is dried. Therefore,since the thin plate material is often cracked or broken by bending, acontact or the like, there arises a problem that the thin plate materialis difficult to handle. Accordingly, a thin natural wood plate materialitself cannot be used without being cracked or broken.

[0006] More specifically, there is a problem that no thin natural woodplate material excellent in folding endurance exists.

[0007] Thus, as the result of earnest studies, the inventors of thepresent invention achieved the present invention in consideration of thefollowing facts: wood, which is not cut yet, has softness and cells ofthe wood are filled with water; dried wood is used as raw wood processedinto a thin plate, and therefore, cells or intercellular spaces of thedried wood are cavities lacking in water; the other cavities such asvessels or sieve tubes are present in the wood; lignin in the woodsolidifies cellulose in the wood as a paste-like substance as the woodis dried; and the like.

DISCLOSURE OF THE INVENTION

[0008] A flexible natural wood sheet recited in claim 1 of the presentinvention is characterized in that a cavity in a thin natural wood platematerial is filled with a polymer compound so as to have foldingendurance.

[0009] Herein, the folding endurance signifies folding endurance asdefined in JIS P 8115.

[0010] The flexible natural wood sheet recited in claim 2 of the presentinvention according to claim 1 is characterized in that the polymercompound is a mixture of a synthetic resin and a linear polymercompound.

[0011] The flexible natural wood sheet recited in claim 3 of the presentinvention according to claim 2 is characterized in that a glasstransition point of the synthetic resin is a room temperature or lower.

[0012] The flexible natural wood sheet recited in claim 4 of the presentinvention according to claim 2 or 3 is characterized in that thesynthetic resin is capable of interacting with a hydroxyl group.

[0013] The flexible natural wood sheet recited in claim 5 of the presentinvention according to any one of claims 2 to 4 is characterized in thatthe synthetic resin contains a hydroxyl group.

[0014] The flexible natural wood sheet recited in claim 6 of the presentinvention according to any one of claims 2 to 5 is characterized in thatthe synthetic resin contains a cellulosic synthetic resin.

[0015] The flexible natural wood sheet recited in claim 7 of the presentinvention according to any one of claims 2 to 6 is characterized in thata molecular weight of the synthetic resin is 1500 to 100000.

[0016] The flexible natural wood sheet recited in claim 8 of the presentinvention according to any one of claims 2 to 7 is characterized in thata vapor pressure of the linear polymer compound at an ambienttemperature is 1.3 kPa or lower.

[0017] The flexible natural wood sheet recited in claim 9 of the presentinvention according to any one of claims 2 to 8 is characterized in thatthe linear polymer compound is capable of interacting with a hydroxylgroup.

[0018] The flexible natural wood sheet recited in claim 10 of thepresent invention according to any one of claims 2 to 9 is characterizedin that the linear polymer compound is polyethylene glycol.

[0019] The flexible natural wood sheet recited in claim 11 of thepresent invention according to claim 10 is characterized in that amolecular weight of polyethylene glycol is 200 to 60000.

[0020] The flexible natural wood sheet recited in claim 12 of thepresent invention according to any one of claims 1 to 11 ischaracterized in that a content of the polymer compound filling thecavity of the thin natural wood plate material is 10% by volume to 95%by volume.

[0021] The flexible natural wood sheet recited in claim 13 of thepresent invention according to any one of claims 1 to 12 ischaracterized in that a thickness of the thin natural wood platematerial is 0.1 mm to 5.0 mm.

[0022] The flexible natural wood sheet recited in claim 14 of thepresent invention according to any one of claims 1 to 13 ischaracterized in that a rebound resilience value of the thin naturalwood plate material is 10 times or less that of an original thin platematerial.

[0023] The above-described objects and the other objects,characteristics and advantages of the present invention will be moreapparent from the detailed description of embodiments of the presentinvention described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic view according to the present invention;

[0025]FIG. 2 is a conceptual view showing before and after cavity cellsare filled with a polymer compound;

[0026]FIG. 3 is a cross-sectional electron microscope photograph of athin natural wood plate material including cavities; and

[0027]FIG. 4 is a cross-sectional electron microscope photograph of athin natural wood plate material according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] The present invention provides a flexible natural wood sheet withsoftness, flexibility, and texture and feeling inherent to natural wood,which has folding endurance obtained by filling cavities present in athin natural wood plate material such as a cavity in a cell, anintercellular space, a vessel or a sieve tube with a polymer compound toovercome the defect that the thin natural wood plate material is likelyto be cracked or broken.

[0029]FIG. 1 is a schematic view of the present invention. Cavityportions in a flexible natural wood sheet 10 are filled with a syntheticresin 20. FIG. 2 is a conceptual view showing cavity cells before andafter being filled with a polymer compound. A cavity portion 30surrounded by a cell membrane 40 is filled with the synthetic resin 20.FIG. 3 is an electron microscope photograph showing a state of cavitiesin a thin natural wood plate material, whereas FIG. 4 is an electronmicroscope photograph showing a state of the cavities filled with thepolymer compound in the present invention.

[0030] As can be seen in FIG. 4, not all the cavities are filled withthe polymer compound.

[0031] A thin natural wood plate material in the present inventionincludes: a rotary veneer; a sliced veneer; a sawn veneer; and ahalf-round veneer, and does not intend to limit the types of naturalwood to be used. For example, white sycamore, birdseye maple, anigre,teak, bamboo and the like are used.

[0032] A thin natural wood plate material to be used has a thickness of0.1 mm to 5.0 mm, preferably, 0.1 mm to 1.0 mm. A veneer having athickness less than 0.1 mm cannot be mechanically fabricated, whereas itis difficult to fill a veneer having a thickness equal to or larger than5.0 mm with a synthetic resin or the like.

[0033] The buffing may also be conducted to control the thickness.

[0034] A polymer compound used for filling the cavities is on the basisof a polymer compound in a rubbery state or an elastic gel state.Example of the polymer compound includes a linear polymer compound onthe basis of a synthetic resin such as a polyester resin, a polyamideresin, a cellulosic resin, a styrene resin, an epoxy resin and aurethane resin.

[0035] As a polyester resin, there are polyethylene terephthalate,polybutylene terephthalate and the like. As a polyamide resin, there arepolyhexamethylene adipamide, polycapramide and the like. As a cellulosicresin, hydroxycellulose, acetylcellulose, nitrocellulose,ethylcellulose, cellulose acetate butyrate, cellulose acetate propionateand the like. As a styrene resin, there are a styrene-acryl nitrilecopolymer, a styrene-butadiene-acrylonitrile copolymer, a styrene-alkylacrylate-alkyl methacrylate copolymer and the like.

[0036] Among these resins, a synthetic resin is preferably capable ofinteracting with a hydroxyl group; for example, a synthetic resin havinga hydroxyl group, an amino group, an ether linkage or the like. In thisregard, a cellulosic synthetic resin and a styrene resin are preferred;for example, hydroxycellulose, acetylcellulose, a styrene-acryl nitrilecopolymer, a styrene-butadiene-acrylonitrile copolymer, a styrene-alkylacrylate-alkyl methacrylate copolymer and the like are preferred. Thisis because these synthetic resins have a hydroxyl group or an etherlinkage and exhibit elasticity in a swollen state.

[0037] Moreover, these synthetic resins are preferred also because theyare on the basis of cellulose which is an element constituting askeletal structure of wood so as to more firmly keep the synthetic resinthrough hydrogen bonds between the wood and the synthetic resin. If thesynthetic resin is cellulosic, a bond other than the hydrogen bonds,i.e., a Van der Waals bond is also conceivable.

[0038] Furthermore, these synthetic resins are preferred also becausewater is adsorbed to the skeletal structure of wood due to the effectsof ambient humidity even though natural wood is dried. It is difficultto completely remove such adsorbed water.

[0039] Various additives may be added to the synthetic resin usedherein. For example, the additives are: a plasticizer; an antistaticagent; a colorant; a filler; a stabilizer; a fire retardant; ananti-oxidant; a UV-protection agent; an aromatizer; and the like.

[0040] It is desirable that a glass transition point of the syntheticresin is a room temperature or lower. If the glass transition point ofthe synthetic resin is a room temperature or lower, the synthetic resinis in a rubbery state exhibiting elasticity at room temperature.Therefore, the flexible natural wood sheet can be prevented from beingcracked or broken. Even if the glass transition point of the syntheticresin itself is higher than a room temperature, such a synthetic resinmay be used as long as its glass transition is lowered to a roomtemperature or lower as a result of addition of an additive.

[0041] A molecular weight of the synthetic resin is preferably 1500 to100000. If the molecular weight is equal to or larger than 100000, thereis a possibility that a brittle fracture may occur. If the molecularweight is equal to or lower than 1500, there is a possibility that thesynthetic resin may exude.

[0042] A mixture of a synthetic resin and a linear polymer compound isused as a polymer compound so as to accelerate the interaction with theskeletal structure of wood as compared with the case where the syntheticresin alone is used, thereby more firmly keeping the synthetic resin.Furthermore, the linear polymer compound or the like makes the syntheticresin swell, so that the synthetic resin exhibits elasticity.

[0043] As a linear polymer compound, there are polyethylene glycol,polyethylene terephthalate, polyhexamethylene adipamide, polyethylene,polypropylene, polyacrylic acid ester, polyvinyl alcohol and the like.However, polyethylene glycol, which can generate hydrogen bonds withcellulose forming the skeletal structure of wood, is preferred for usein the present invention. When such a substance is sorbed to a woodmaterial, the skeletal structure of wood swells so as to be easilyfilled with a synthetic resin. At the same time, the softness isincreased because of wetting, resulting in improved processibility.

[0044] Moreover, since polyethylene glycol interacts not only with theskeletal structure of wood but also with the synthetic resin to be used,it is considered that polyethylene glycol acts like a clamp on thesynthetic resin and the skeletal structure of wood.

[0045] The linear polymer compound for use may be an oligomer or apleionomer.

[0046] The oligomer is situated between the monomer and the polymer,with a molecular weight of 1000 to 100000. The pleionomer is an oligomerhaving a large molecular weight.

[0047] Even a linear polymer material having a molecular weight of 1000or less can be used as long as it interacts with the skeletal structureof wood or a synthetic resin. For example, polyethylene glycol having amolecular weight of 200 can be used.

[0048] With a small molecular weight, the linear polymer material islikely to be diffused. This makes the skeletal structure of wood or thelike easily swell, facilitating the control of swelling by the usage.

[0049] It is desirable that a vapor pressure of the linear polymercompound at an ambient temperature is 1.3 kPa or lower. If a vaporpressure at an ambient temperature is high, the substance is evaporatedfrom the skeletal structure of wood. As a result, since the wood isbrought into the same state as that of dried wood, it is likely to becracked or broken.

[0050] Moreover, a linear polymer compound is sometimes decomposedinstead of being evaporated. In this case, the linear polymer compounddoes not exhibit any vapor pressure.

[0051] As a method of filling the synthetic resin and the linear polymercompound, there are: a method of immersing a thin plate material into asolution containing the two; a method of spraying the solution; atwo-step method for immersing a thin plate material into differentsolutions respectively containing the synthetic resin and the linearpolymer; a method of polymerizing a monomer of the resin after filling;an immersing process followed by coating; and the like. However, themethod is not limited thereto.

[0052] Although there are a pad-roll method, a coating method, aprinting method and the like as a coating method, the method is notlimited thereto.

[0053] Furthermore, the number of processes of immerse, spraying,coating and the like is not limited.

[0054] A thin natural plate material may be treated with water-solublecellulose, for example, such as carboxymethyl cellulose before beingfilled with the synthetic resin and the linear polymer compound. This isbecause it is considered that a bond between wood cellulose and thesynthetic resin or the like can be reinforced thereby.

[0055] Cavities in the thin plate material are filled with the syntheticresin and the linear polymer compound at a ratio of 10% by volume to 95%by volume.

[0056] If the filling ratio is 10% by volume or less, a crack is likelyto occur when the thin plate material is bent. If the cavities areintended to be filled at a ratio of 95% by volume or higher, it takeslong time to fill the cavities. Therefore, substantial productionthereof is difficult.

[0057] A rebound resilience value of the thin natural wood platematerial is preferably 10 times or less that of an original thin platematerial, more preferably, 5 times or less. If the rebound resiliencevalue of the thin natural wood plate material exceeds 10 times that ofthe original thin plate material, the texture and feeling inherent tothe thin natural wood plate material differ from those of the originalthin plate material. Therefore, the texture or the feeling of theoriginal plate material cannot be perceived any more. Herein, therebound resilience value is obtained according to a method in JIS L 1096A (Gurley method).

[0058] A flexible natural wood sheet according to the present inventionmay be backed with a backing material such as Japanese paper, paper,synthetic paper, butter muslin, non-woven fabric, canvas, a pig skin, asynthetic resin sheet or the like so as to further reinforce thestrength. These backing materials may be attached by a normal method.

[0059] The use of a backing material improves the dimensional stability,folding endurance and the like.

[0060] Hereinafter, the present invention will be described in examples.The present invention is not limited to the examples.

EXAMPLE 1

[0061] A solution obtained by dissolving 1.18 kg of polyethylene glycolhaving a molecular weight of 4000 into 10 L of ethanol was prepared.White sycamore lumber having a thickness of 0.17 mm was heated in thesolution at 180° C. for 10 minutes, and then was heated at 120° C. for 5minutes in a solution obtained by dissolving 0.89 kg of hydroxycellulosehaving a molecular weight of 60000 into 10 L of ethanol. After theheating treatment, the white sycamore lumber was washed with water andthen dried. A filling ratio after drying was measured to be 58% byvolume.

[0062] The characteristic values of the thus obtained thin natural woodplate material are shown in Table 1. TABLE 1 Test Result The Commer-Commer- Present Raw cial cial Testing Test Item Invention Wood Product AProduct B Method Rebound 17.2 4.3 65.8 48.8 Method Resilience accordingto (mN) JIS L 1096 A (Gurley method), only in a longitudinal directionFolding 1000 or 0 28 6 JIS P 8115, Endurance more Longitudinal (times)direction Folding 1000 or 0 85 15 JIS P 8115, Endurance more Horizontal(times) direction

[0063] As is apparent from Table 1, the thin natural wood plate materialaccording to the present invention has rebound resilience close to thatof the raw wood as compared with the commercial products, exhibitingsoftness. The rebound resilience was measured by a method according toJIS L 1096 A (Gurley method).

[0064] Moreover, the thin natural wood plate material according to thepresent invention exhibits toughness against breakage with the foldingendurance of 1000 times or more in both the longitudinal and thehorizontal directions. The folding endurance was measured according to amethod as defined in JIS P 8115.

[0065] It is considered that the above results are obtained because thethin plate material according to the present invention is filled withthe synthetic resin and the linear polymer compound to exhibitelasticity; the synthetic resin and the like filling the plate materialhave the buffering effects.

[0066] On the other hand, it is considered that any improvement infolding endurance is not observed in the commercial products becausethey do not have such buffering effects.

[0067] As comparative examples, a thin raw wood plate without anytreatment, commercial raw wood on which a film is attached (commercialproduct A), and coated commercial raw wood (commercial item B), eachhaving the same thickness, were used.

Examples 2 to 5

[0068] In a solution of 500 g of polyethylene glycol having a molecularweight of 200, 2.1 g of birdseye maple lumber having a thickness of 0.15mm (200 mm by 100 mm) was immersed at a room temperature for 5 minutes.After removal of polyethylene glycol adhered to the surface, the lumberwas coated by coating with an emulsion solution containing 20 parts byweight of a styrene-acryl copolymer resin (XA-4650 by TohpeCorporation), 20 parts by weight of an acrylic copolymer resin (XA-4663Aby Tohpe Corporation) and 4 parts by weight of water so that thequantity of a solid content after drying became 25 g/m². Furthermore,the lumber was coated by coating with a solution containing 100 parts byweight of an urethane resin (FF urethane mat clear 78-29 by Union PaintCo. Ltd.), 10 parts by weight of an urethane resin hardener (urethanehardener B-300 by Union Paint Co. Ltd.) and 22 parts by weight of athinner so that the quantity of a solid content after drying became 22g/m². Based on a density of polymers and a cavity ratio of the birdseyemaple lumber, a filling ratio of the thus fabricated thin natural woodplate material was measured to be 90% by volume. By controlling theimmersion time into ethylene glycol and the number of coating of thestyrene-acryl copolymer resin, the acrylic copolymer resin and theurethane resin, thin natural wood plate materials having differentfilling ratios were obtained (respectively at 10% by volume, 30% byvolume and 50% by volume).

[0069] The characteristic values of the thus obtained thin natural woodplate materials are shown in Table 2. TABLE 2 Test Result 10% by 30% by50% by 90% by Testing Test Item volume volume volume volume MethodRebound 19.3 24.2 28.1 29.7 Method Resilience according to (mN) JIS L1096 A (Gurley method), only in a longitudinal direction Folding 10 86368 1090 JIS P 8115, Endurance Longitudinal (times) direction

[0070] The rebound resilience is measured by a method according to JIS L1096 A (Gurley method), and the folding endurance is measured as definedin JIS P 8115.

[0071] As is apparent from Table 2, the thin natural wood plate materialaccording to the present invention is soft and has folding enduranceeven at a low filling ratio.

[0072] When wood, which is a naturally-occurring polymer, is dried,water in the cells is evaporated. As a result, the wood is constitutedby holes such as vessels continuously penetrating through the structure,cell membranes lacking in water and the like. Since the cell membraneconsists of cellulose forming the skeletal structure, hydrogen bonds aregenerated between cellulose of the cell membrane and the synthetic resincapable of forming hydrogen bonds when the cavities are filled with thesynthetic resin. Therefore, the synthetic resin hardly comes off thecavities.

[0073] Moreover, since the linear polymer compound wets celluloseforming the skeletal structure of the cell membrane and makes it swell,the linear polymer compound has the effect of facilitating the fillingof the synthetic resin. Furthermore, swelling of cellulose forming theskeletal structure and the synthetic resin filling the cavities makescellulose be in contact with the synthetic resin, which prevents thesynthetic resin from coming off. FIG. 2 shows a conceptual view thereof.

[0074] Furthermore, the synthetic resin and the linear polymer compoundin the present invention are both capable of forming hydrogen bonds.Therefore, the linear polymer compound has the effect of acting as aclamp to bond the synthetic resin and cellulose with each other.

[0075] On the other hand, since the vapor pressure of the linear polymercompound at an ambient temperature is low, it wets cellulose andmaintains a swollen state without being evaporated at an ambienttemperature. Therefore, the linear polymer compound has the effect ofmaintaining the flexible natural wood sheet in a soft state.

[0076] Furthermore, when the used synthetic resin swells, it exhibitselasticity. Therefore, the synthetic resin also has the effect ofimparting flexibility to the flexible natural wood sheet.

[0077] The results of the tests clearly show that the flexible naturalwood sheet according to the present invention overcomes the disadvantageof a raw thin natural wood plate material that it is easily cracked orbroken so as to have softness and resistance in view of foldingendurance. Therefore, the flexible natural wood sheet is soft and haspeculiar effects in terms of folding endurance. Thus, even in the casewhere the flexible natural wood sheet is to be sewn, it is not easilycracked or broken as a conventional thin natural wood plate material.Therefore, it is expected that the flexible natural wood sheet isapplied in the field where it can be sewn or stitched.

[0078] Moreover, since the surface is not entirely covered with thesynthetic resin or the like, the texture and feeling inherent to naturalwood remain to allow the humidity control effects of natural wood to bedemonstrated. Thus, the healing effects are expected to be obtainedthereby.

[0079] On the other hand, the cavities in the thin natural wood platematerial are filled with the synthetic resin. Therefore, since theflexible natural wood sheet is not natural wood without any treatment,it has the effects that the flexible natural wood sheet hardly rots.

INDUSTRIAL APPLICABILITY

[0080] As described above, the flexible natural wood sheet according tothe present invention has folding endurance and therefore is hardlycracked or broken by repetitive bending. Therefore, in addition to theapplications as a wall paper, a decorative sheet and the like, theflexible natural wood sheet can be used for a bag, a hand bad, a roll-upblind, a material for pocketbook, a covering material for home electricappliances, a material for shoes, a home finishing material for roominterior, an interior finishing material for vehicles includingautomobiles and the like.

[0081] Since the flexible natural wood sheet has flexibility, forexample, it can also be used to cover an object having a curved surface,for example, the exterior of a metal pipe. Moreover, the flexiblenatural wood sheet also has the effect that it can be used even at alarge curvature owing to the flexibility.

1. A flexible natural wood sheet, comprising a polymer compound filledinto a cavity in a thin natural wood plate material so as to providefolding endurance.
 2. The flexible natural wood sheet according to claim1, wherein the polymer compound is a mixture of a synthetic resin and alinear polymer compound.
 3. The flexible natural wood sheet according toclaim 2, wherein a glass transition point of the synthetic resin is atroom temperature or lower.
 4. The flexible natural wood sheet accordingto claim 2, wherein the synthetic resin is interacts with a hydroxylgroup.
 5. The flexible natural wood sheet according to claim 2, whereinthe synthetic resin includes a hydroxyl group.
 6. The flexible naturalwood sheet according to claim 2, wherein the synthetic resin includes acellulosic synthetic resin.
 7. The flexible natural wood sheet accordingto any one of claims 2 to 6, a molecular weight of the synthetic resinis about 1,500 to about 100,000.
 8. The flexible natural wood sheetaccording to claim 2, wherein a vapor pressure of the linear polymercompound at an ambient temperature is about 1.3 kPa or lower.
 9. Theflexible natural wood sheet according to claim 2, wherein the linearpolymer compound interacts with a hydroxyl group.
 10. The flexiblenatural wood sheet according to claim 2, wherein the linear polymercompound is polyethylene glycol.
 11. The flexible natural wood sheetaccording to claim 10, wherein a molecular weight of polyethylene glycolis about 200 to about 60,000.
 12. The flexible natural wood sheetaccording to claim 1, wherein a content of the polymer compound fillingthe cavity of the thin natural wood plate material is about 10% byvolume to about 95% by volume.
 13. The flexible natural wood sheetaccording to claim 1, wherein a thickness of the thin natural wood platematerial is about 0.1 mm to about 5.0 mm.
 14. The flexible natural woodsheet according to claim 1, wherein a rebound resilience value of thethin natural wood plate material is about 10 times or less that of anoriginal thin plate material.